| 1. |
- Benko, Gabor, et al.
(författare)
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Interligand electron transfer determines triplet excited state electron injection in RuN3-sensitized TiO2 films
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:9, s. 2862-2867
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Tidskriftsartikel (refereegranskat)abstract
- Electron injection from the transition metal complex Ru(dcbpy)(2)(NCS)(2) (dcbpy = 2,2'-bipyridine-4,4'-dicarboxylate) into a titanium dioxide nanoparticle film occurs along two pathways. The dominating part of the electron injection proceeds from the initially excited singlet state of the sensitizer into the conduction band of the semiconductor on the sub-hundred-femtosecond time scale. The slower part of the injection occurs from the thermalized triplet excited state on the picosecond time scale in a nonexponential fashion, as was shown in a previous study (Benko, G.; et al. J. Am. Chem. Soc. 2002, 124, 489). Here we show that the slower channel of injection is the result of the excited state being localized on a ligand of the sensitizer that is not attached to the semiconductor; hence, the electron cannot be injected directly from such an excited state into the semiconductor. Before being injected, it has to be transferred from the non-surface-attached ligand to the attached one. The results show that the interligand electron-transfer time is on the picosecond time scale, depends on the relative energies of the two ligands, and controls the electron injection from the excited triplet state of the sensitizer. The findings provide information relevant to the design of molecular-based assemblies and devices.
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| 2. |
- Kallioinen, J, et al.
(författare)
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Photoinduced ultrafast dynamics of Ru(dcbpy)(2)(NCS)(2)-sensitized nanocrystalline TiO2 films: The influence of sample preparation and experimental conditions
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:20, s. 6365-6373
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Tidskriftsartikel (refereegranskat)abstract
- In most of the previous ultrafast electron injection studies of Ru(dcbpy)(2)(NCS)(2)-sensitized nanocrystalline TiO2 films, experimental conditions and sample preparation have been different from study to study and no studies of how the differences affect the observed dynamics have been reported. In the present paper, we have investigated the influence of such modifications. Pump photon density, environment of the sensitized film (solvent and air), and parameters of the film preparation (crystallinity and quality of the film) were varied in a systematic way and the obtained dynamics were compared to that of a well-defined reference sample: Ru(dcbpy)(2)(NCS)(2)-TiO2 in acetonitrile. In some cases, the induced changes in the dynamics were uncorrelated to the electron injection process. High pump photon density (not in the linear response region) and exposure of the sensitized film to air altered the picosecond-time- scale kinetics considerably, and the changes were attributed mostly to degradation of the dye. In other cases, changes in the measured kinetics were related to the electron injection processes: reducing the firing temperature of the nanocrystalline film or making the film via electron beam evaporation (EBE) resulted in a decrease of the overall crystallinity of the film, and the electron injection slowed. In the sensitized EBE films, in addition to an increased contribution of triplet excited-state electron injection, a new electron transfer (ET) process with a time constant of 200 fs was observed.
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| 3. |
- Laaksonen, L., et al.
(författare)
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Comparative effects of dexmedetomidine, propofol, sevoflurane, and S-ketamine on regional cerebral glucose metabolism in humans : a positron emission tomography study
- 2018
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Ingår i: British Journal of Anaesthesia. - : Elsevier. - 0007-0912 .- 1471-6771. ; 121:1, s. 281-290
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: The highly selective α2-agonist dexmedetomidine has become a popular sedative for neurointensive care patients. However, earlier studies have raised concern that dexmedetomidine might reduce cerebral blood flow without a concomitant decrease in metabolism. Here, we compared the effects of dexmedetomidine on the regional cerebral metabolic rate of glucose (CMRglu) with three commonly used anaesthetic drugs at equi-sedative doses.Methods: One hundred and sixty healthy male subjects were randomised to EC50 for verbal command of dexmedetomidine (1.5 ng ml-1; n=40), propofol (1.7 μg ml-1; n=40), sevoflurane (0.9% end-tidal; n=40) or S-ketamine (0.75 μg ml−1; n=20) or placebo (n=20). Anaesthetics were administered using target-controlled infusion or vapouriser with end-tidal monitoring. 18F-labelled fluorodeoxyglucose was administered 20 min after commencement of anaesthetic administration, and high-resolution positron emission tomography with arterial blood activity samples was used to quantify absolute CMRglu for whole brain and 15 brain regions.Results: At the time of [F18]fluorodeoxyglucose injection, 55% of dexmedetomidine, 45% of propofol, 85% of sevoflurane, 45% of S-ketamine, and 0% of placebo subjects were unresponsive. Whole brain CMRglu was 63%, 71%, 71%, and 96% of placebo in the dexmedetomidine, propofol, sevoflurane, and S-ketamine groups, respectively (P<0.001 between the groups). The lowest CMRglu was observed in nearly all brain regions with dexmedetomidine (P<0.05 compared with all other groups). With S-ketamine, CMRglu did not differ from placebo.Conclusions: At equi-sedative doses in humans, potency in reducing CMRglu was dexmedetomidine>propofol>ketamine=placebo. These findings alleviate concerns for dexmedetomidine-induced vasoconstriction and cerebral ischaemia.
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| 4. |
- Frankenberg, Sofia J., et al.
(författare)
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Bidirectional collaborations in an intervention randomized controlled trial performed in the Swedish early childhood education context
- 2019
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Ingår i: Journal of Cognition and Development. - : Informa UK Limited. - 1524-8372 .- 1532-7647. ; 20:2, s. 182-202
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Tidskriftsartikel (refereegranskat)abstract
- Within the field of developmental science, there is a general agreement of the need to work together across academic disciplinary boundaries in order to advance the understandings of how to optimize child development and learning. However, experience also shows that such collaborations may be challenging. This paper reports on the experiences of bidirectional collaboration between researchers in a multidisciplinary research team and between researchers and stakeholders, in the first randomized controlled trial in Swedish preschool. The objective of the trial was to investigate the effects of two pedagogical learning strategies evaluating language, communication, attention, executive functions and early math. The interdisciplinary team includes researchers from early childhood education, linguistics, developmental psychology and cognitive neuro science. Educational researchers and theorists within the field of early childhood education in Sweden have during the last two decades mainly undertaken small-scale qualitative praxis-oriented and participative research. There is a widespread skepticism with regards to some of the core principles in controlled intervention methodologies, including a strong resistance towards individual testing of children. Consequently unanticipated disagreements and conflicts arose within the research team, as RCT methodology requires the measurement of effects pre and post the intervention. The aim of this article is to discuss the conditions for bidirectional collaboration both between researchers and stakeholders and between researchers in the research team. The findings illustrate strategies and negotiations that emerged in order to address ontological and epistemological controversies and disagreements. These include (a) the negotiation of research ethics, (b) making divergences visible and learning from each other, (c) using a multi-epistemological and methodological approach as a complement to the RCT design and (d) the negotiation of research problems that are shared between educators and researchers.
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